26 



powder, or other cleansing powder. They should then 

 receive a final rinsing and be placed in a suitable rack to 

 drain. 



DETERMINATION OF TOTAL SOLIDS IN MILK. 



As brought out earlier in this circular, milk is composed 

 of water and the various solids collectively known as total 

 solids or milk solids. Manifestly the simplest way of 

 determining the amount of total solids in a given quantity 

 of milk is to separate them from the 

 water and weigh them. This is pre- 

 cisely the manner in which the total 

 solids in milk are determined in the 

 laboratory. A small quantity of milk 

 is weighed into a shallow flat-bottomed 

 dish and then heated until all the water 

 is driven off. During this evaporation 

 the milk must not be heated more than 

 a degree or so above the boiling point 

 of water, because at a higher tem- 

 perature some of the solids are decom- 

 posed. 



Ovens. Several types of ovens are used for holding the 

 milk at the right temperature during the evaporation. 

 The simplest type is perhaps the so called double-walled 

 drying oven (fig. 23). This piece of apparatus is really one 

 oven inside of another, the space between the two being 

 partly filled with water. A burner placed under the oven 

 boils the water, and the remaining space between the 

 walls is filled with steam, maintaining a constant tempera- 

 ture in the inner compartment which holds the milk 

 dishes. Unless carefully watched, the oven will "boil 

 dry," to prevent which it is a good plan to attach some 

 sort of condenser. The type of condenser known as the 

 globe condenser is very satisfactory for this purpose. Some 

 ovens are constructed with a constant-level attachment. 



Balance. Nice weighings are required in the determi- 

 nation of total solids in milk, and it is necessary to use the 



FIG. 22. Jar 

 with per- 

 forated cover 

 for use in 

 emptying test 

 bottles. 



